Electric power controllers

ABSTRACT

A power controller for controlling the intermittent supply of current to a load, such as a cooker hotplate, has a pivotally mounted snap switch controlled by a heated bimetal member which is heated in dependence upon the connected power. A compensating bimetal strip, for taking ambient temperature into account, is arranged on the snap switch and parallel thereto. A control cam acts on the free end of the compensating bimetal strip. The latter is shielded from the heat of the heated bimetal member.

The invention relates to a power controller for the controllable supplyof electrical power in power pulses to a load, having a workingbimetallic member, which is heated in dependence upon the connectedpower and which acts upon a snap switch.

A power controller is described in the publication"Conti-Elektro-Berichte" (Conti-Electro-Reports), October/December 1959,Pages 285 to 290. The power controller illustrated in FIG. 3 on page 285of this publication has a working bimetal strip to which a compensatingbimetal strip is connected at right angles. In the region of theinternal corner between these two bimetal strips is pivotably mounted ona pin disposed in the switch socket. The compensating bimetal strip actsupon an encapsulated switch. Adjustment is effected by means of acontrol cam which acts upon the free end of the working bimetal strip byway of a roller, a separately mounted lever and an adjusting screw. Amechanical switch with two contact springs is disposed opposite thebimetal strip.

For structural reasons the bimetal strip of such a controller can onlyhave a length which is not much longer than half the switch dimensions.Consequently its thickness dimension and its working travel are thenalso smaller. In addition, the heat of the bimetal strip is transferredto the directly attached compensating bimetal strip so that thiscompensating bimetal strip operates constantly in a range of relativelyhigh temperature and its actual object, the taking into account theinfluence of ambient temperature, can only be partially achieved.Adjusting the working region by pivoting the working bimetal strip withthe aid of a lever mechanism is a complicated task and leads to thereproducibility of the individual part loads being inaccurate. Inparticular, this reproducibility is poor in the critical upper and lowerpower ranges. A part load of, for example, 5% , which is necessary to beable to heat up an electric hotplate, cannot be positively controlledwith such a controller.

Power controllers with a pivotable snap switch have been described, forexample, in German Patent specification No. 16 40 084. The bimetal striptherein is directly connected to the snap spring and the control iseffected by way of a cam disc and a lever having a stop whose distancerelative to the working bimetal strip is adjusted during the adjustingprocess. This system permits the use of only relatively thin and labilebimetal strips and presents problems with the addition of a compensationdevice, not envisaged in this publication.

An object of the invention is to provide a power controller which iseasy to manufacture on a small scale and enables the power settings tobe reproduced very well despite relatively low requirements being set onthe precision of the construction. In particular, the compensation forthe ambient temperature is to be reliably achieved.

According to the present invention, a power controller for thecontrollably intermittant supply of electrical power to a load,comprises a pivotably mounted bimetal member, means for heating thelatter in dependence upon the connected power, a pivotally mounted snapswitch for the load current, the bimetal housing a lever which extendsat an angle thereto and which acts upon the snap switch, a compensatingbimetal strip secured to the snap switch and extends substantiallyparallel to the snap switch at one side thereof, and a control cam whichacts upon the free end of the compensating bimetal strip.

A compensating bimetal/snap switch unit is therefore formed which isjointly pivotable. The compensating bimetal strip is only influenced toa very small extent by the temperature of the working bimetal member andcan therefore achieve its task of compensation. Moreover, it is alsoheat-shielded by the snap switch lying parallel thereto. It may be shortand relatively strong. However, the working bimetal member alwaysremains in its position and only one of its ends pivots towards the snapswitch in accordance with the extent of its heating.

For this purpose, the bimetal member is preferably L-shaped, the longerbimetal limb being provided with a heating device and being possiblysupported on the housing by way of an adjusting screw under springforce.

According to a further feature of the invention, provision is made for adiode to be provided in a controller to be operated with alternatingcurrent, the diode being connected in circuit with the heating devicefor the bimetal member by a switch, actuable by the adjusting shaft,only in the upper power range and being disconnected in the lower powerrange.

A relatively large-dimensioned bimetal heating device, which isconsequently less influenced by the wire gauge, may therefore beprovided. In the lower power range this heating device is fullyeffective so that the bimetal member quickly heats up, resulting in theoverall power being quickly disconnected. The resultant short relativeconnection period also keeps the heating of the switch within limitssince the bimetal control heating device is only switched on during theconnection of the load. However, in the upper power range which maybegin, for example, at 20% relative connection period, the diode isconnected in series with the bimetal heating device. The heating deviceof the bimetal thereby only ever receives a half-wave of the alternatingcurrent and thus only half the power. Consequently the development ofheat is less and the higher outputs are easier to control. In thisregion, the development of heat would be particularly unwelcome becausethere is a long connection period here also for the bimetal heatingdevice. In addition, the temperatures at the bimetal are kept low andthe entire switch heating remains low so that the ambient temperaturecan also be compensated for advantageously.

It is particularly preferable for the diode at the rear side of thehousing of the power control apparatus remote from the operated side tobe disposed directly on the switch which bridges it. Such an embodimentkeeps the expense for the arrangement and switching in circuit of thediode very low and the diode is disposed in the cool external region ofthe switch. The switch connecting the diode may be a simple creepingswitch which does not need any snap mechanism in the adjusting shaft.

The invention will be further described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a plan view of one embodiment of a power controller accordingto the invention, seen from the operated side, with a closure coverremoved;

FIG. 2 is a section along the line II--II in FIG. 1;

FIG. 3 is a rear view of the power controller of FIG. 2, seen from theleft; and

FIG. 4 is a schematic circuit diagram of the power controller shown inFIGS. 1 to 3.

One embodiment of power controller 11 is shown in FIGS. 1 to 3. It has arear housing part 12 (or housing part remote from the operated side)made of plastics material and in the form of a rectangular or preferablysquare block with an internal cavity 25. This cavity is sealed by aplate-shaped cover 13 which faces towards the operated side and hascentering dowels 17 which engage in centering recesses 16 on the housingpart 12. A screw-threaded bush 14 is secured to the cover 13 and anadjusting shaft 15, which carries an adjusting knob 60 indicated in FIG.4, protrudes through the threaded bush. The adjusting shaft 15 protrudesinto a central hole 23 in a control body 18 which is made of insulatingmaterial and carries on its outer periphery a control cam 19 and aswitching cam 20. At its end remote from the operated side, the controlbody 18 has a bearing pin 21 which protrudes through an aperture 24 inthe rear housing part 12 and comprises a further switching cam 22 on therear side of the housing part 12.

A compensating bimetal strip 26 co-operates with the control cam 19,this compensating bimetal strip being in the form of a transmissionlever which has a front curved end by which the bimetal strip 26 ispressed against the control cam 19 under the force of a spring 34. Thecompensating bimetal strip 26 is relatively thick and rigid and ispivotably mounted by its end opposite the front curved end by which itabuts the control cam 29 by means of a pivot 28. At this end, thecompensating bimetal strip is attached to a switch carrier 29 of a snapswitch 27, so that the compensating bimetal strip is parallel to theswitch carrier 29 and is slightly spaced therefrom. The snapswitch/compensating bimetal unit is therefore pivotable as a whole aboutthe pivot 28.

Disposed on the switch carrier 29 is a snap spring which is supported inthe conventional manner on a support bearing and which has a bowedresilient tongue under buckling stress. The snap spring carries at itsfree end its contact 31, which co-operates with a fixed counter-contact32, and is fixed at its opposite end by an adjusting screw 33, which hasan annular groove into which a fork-like end of the snap spring isinserted. A terminal end of an electrical supply line 35 is welded toone fork end whereby the snap spring is electrically connected to aterminal 68 for a load 70, such as a cooker hotplate element.

The snap switch 27 is actuated by a bimetallic member 36 which isL-shaped. This L is completely made of bimetal strip and a pivot 37 ismounted in the internal angle of the L, this pivot, like the pivot 28,being advantageously journalled in recesses which are locatedrespectively in the housing part 12 and the cover 13 and in which thepivot ends are received when these two housing parts are assembledtogether.

The long, heated limb 38 of the bimetallic member 36 carries a heatingwinding or coil 39 which is supplied with current by way of two supplyleads. An adjusting screw 40 which is pressed by a spring 41 against aninner intermediate wall 42 of the housing part 12 is screwed into thefree end of the heated limb 38.

At the end of the short limb 43 of the bimetallic member 36 there is acranked portion 44 which presses against the actuating point of the snapspring 30.

The heated limb 38 of the bimetallic member 36 is located in a chamber71 which is partially sealed off by the intermediate wall 42 and isventilated by ventilation slots 45.

It can be seen that the snap switch/compensation bimetal unit, on theone hand, and the bimetallic member 36, on the other hand, are disposedat an angle to one another and enclose the control body 18 therebetween.In the corner of the housing cavity 25 opposite this angle, a mechanicalswitch is disposed which has a switch slide 50 actuated by the switchingcam 20. This switch slide 50 is made of plastics material and has theform of a rectangular rod, one of whose ends is rounded off toco-operate with the switching cam 20 and a compression spring 54 actsupon its other end. The switch slide 50 extends substantially diagonallyso that it can have the greatest possible length with the smallest spacerequired.

On its upper and lower face, the switch slide has projections 51 whichform abutments for contact arms 52,53 which are pushed onto the switchslide and protrude beyond it on both sides. The switch slide 50preferably comprises an insulating member so as to be able to push upthe contact arms and secure them by snapping open. Each contact armcarries a contact on each of its two ends.

The switch slide 50 is guided by guides 55 which have the form of metalplates which protrude from the base of the housing part 12 and aredirected at right angles to the switch slide. Four guides 55 areprovided, each two of which lie opposite one another. They guide theswitch slide and partially overlap it. Some of these guides 55 carryfixed contacts 56 and the guides 55 protrude through the base of thehousing part 12 to form connection lugs of the AMP plug-in lug type onthe rear side.

The rear side of the power controller 11 can be seen in FIG. 3. Thisshows that the switching cam 22 cooperates with a switch 61, which is ofvery small and easy construction, in the form of a contact spring whichis designed to short-circuit a diode 62. In this case, the diode issoldered by its connections 63, 64 directly onto the associatedconnecting plug or the contact spring, and the contact spring isembraced by the connection 63 and can short-circuit the diode 62 bytouching its connection 64.

The power controller operates as follows:

In FIG. 1, the disconnected state is shown wherein the switching cam 20has pressed the switch slide 50 back against the force of thecompression spring 54 and has thus removed the contact arm 52 for thesignal pilot light contact and the contact arm 53 for the disconnectionof the second pole from the appropriate fixed contacts. When the controlbody 18 or the adjusting shaft is in this position, the compensatingbimetal strip 26 is located in a recess in the control cam 19 so thatthe control body is positively held in this "off" position.

When the "energy regulator" is connected (by turning the control body 18in a clockwise direction), the control cam 20 first of all releases thecontrol slide 50 which, under the force of the spring 54, applies itscontact arms 52, 53 which are at least partially resilient against theguides 55 such that they are bridged. On the one hand, therefore, thesignal contact line 66, 67 is closed and, on the other hand, one pole ofthe load 70, for example the heating element of an electric hotplate, isclosed.

Because of the action of the spring 34, the compensating bimetal/snapswitch unit pivots into its position which corresponds to the respectiveposition of the control cam 19. The contacts 31 and 32 are closed, sothat the bimetallic member 36 is heated by its heating winding 39. Theswitch 61 is closed in the lower power range, for example when theadjusting shaft is in a position corresponding to power values between 5and 20% of the total power. With a low set power, therefore, the diode62 is bridged so that the full heating power of the heating winding 39is effective.

Consequently, the limb 38 of the bimetallic member 36 deflectsrelatively quickly and presses upon the snap switch in the disconnectingdirection by way of the short limb 43 and the cranked portion 44, sothat this snap switch is opened again after a relatively short time.

After the bimetallic member has cooled down, the snap switch 27re-closes and the working process starts again. In the upper operatingrange, on the one hand, the compensating bimetal/snap switch unit isswivelled further in an anti-clockwise direction and, on the other hand,the diode is effective because of the opening of the switch 61. Theheating winding 39 is therefore only operated with a respectivehalf-wave of the alternating current, i.e. with half the heating power.The bimetal member therefore needs substantially longer to be deflectedto such an extent that it can open the snap switch and thus disconnectthe power supply to the load 70. At the very high temperatures of thebimetal member, the cooling down process is also effected more quicklyso that a longer relative connection period is ensured.

The power controller as described and illustrated has numerousadvantages: Despite its clear and reliable construction, it can beproduced at relatively low building cost and operates with relativelylarge paths and forces for the switching process. In particular, thehigh forces are essential. They are obtained because of the rather largedimensions of the bimetal member. Because of the favourable structure,the working bimetal member may be rather long and the compensationbimetal strip may be rather short and strong. The entire system ispositively moved by the springs 34, 41 into a specific position so thatthere is only one point at which play may occur, namely the point ofcontact between the snap spring 30 and the bowed portion 44 of theworking bimetal member 36.

There is a further advantage in constructing the bimetal member 36 as anL-shaped member made from bimetal strip. Normally it is very difficultto compensate such a controller by a compensating bimetal strip becausethe two bimetal strips operate within different temperature ranges. Thedeflection path of a bimetal strip per unit of temperature does,however, decrease with rising temperature so that the compensation canonly ever be accurate for one working range. The bimetal memberdescribed here, however, has, so to speak, a double heating device. Theshort limb 43 runs parallel to the snap spring 30 at a relatively smalldistance therefrom. This spring is supplied with current by way of thesupply line 35 and is relatively thin. It is therefore heated whencurrent flows through it, even though to a certain extent. This heatadditionally heats the short limb 43, but noticeably only at higherstages because, otherwise, the snap spring would hardly rise aboveambient temperature. However, the negative effect of the deflectionpath, which is regressive with the temperature, is thereby conpensatedfor or counteracts this negative phenomenon.

Accordingly, substantially stepless manual control is provided over allcontrol ranges. Although a small "step" occurs when the diode isswitched on or off, the effect is diminished by a corresponding slope inthe cam, as shown in FIG. 1.

The compensating bimetal strip is, however, shielded from thetemperature as much as possible. It is perpendicular to the workingbimetal member 36 and has no heat conductive connection therewith. It isalso largely shielded relative to the hot chamber by the intermediatewall 42. It is protected from the temperature produced by the snapspring by the switch carrier 29. This arrangement therefore ensures thatthe compensating bimetal strip can actually fulfil the purpose for whichit is intended, namely to effect a compensation for the variable ambienttemperature, and must not operate in a temperature which issubstantially high relative to the surroundings.

The working bimetal member and the compensating bimetal/snap spring unittake up two sides of the switch housing so that one corner remainsentirely free for the switch 50 to 56. The arrangement of this verysmall-built switch in the same radial plane as the other parts of thepower controller enables this controller to be produced with a verysmall structural dimension. The depth in the direction of the adjustingshaft may, for example, be less than 25 mm so that it is also possibleto install it with a vertical shaft in very flat cooking troughs.

The behaviour of the power controller is very positively influenced bythe diode 62. The middle power range is rarely a problem for suchcontroller. The real problem lies in the upper power range and inparticular, however, in the lower power range. In the case of today'shotplates with relatively high power, however, the lower power range isin fact critical when it is also desirable to heat up the hotplate.Outputs of up to 5% of the total power and below (100 W with a 2000 Whotplate) must be positively controlled. However, this requires veryhigh outputs on the bimetal member because this has to react veryquickly. These high outputs would, however, not only heat the controllervery intensely in the higher power range and use energy, but also raisethe temperatures at the bimetal member inadmissibly. This problem can beeasily solved by the advantageous no-loss regulating down of the bimetalheating power, consequently without any lost heat, by means of thediode. The high power, for which the bimetal heating winding isdesigned, is no disadvantage because this is only ever used in the lowerpower range and the relative connection periods there are of course onlyvery short. The heating of the controller by the heating winding 39 istherefore very low. Conversely, the power in the high power range islimited by the diode so that the heating of the switch also remainswithin limits during the relatively long connection periods there.Another advantage is that the heating winding 39 may be simplyconstructed. If it was desirable to make the power less, then problemswould arise because the resistance wires for the low outputs wouldbecome very thin with mains voltage and especially in the case of highermains voltages, thereby also causing the operational reliability tosuffer.

We claim: .[.1. A power controller for the controllable supply ofelectrical power intermittently to a load, comprising: pivots isreceived..]. .[.8. A controller according to claim 7, in which one ofthe housing parts has a cavity which accommodates said snap switch, saidbimetal member, said heating means and said compensating bimetal strip,and the other of said housing parts comprising a cover whichsubstantially closes off said cavity..]. .[.9. A controller according toclaim 1, in which said control cam means has a rotatable adjusting shaftand in which a mechanical mains switch is arranged in said housingsubstantially in the same plane as said snap switch and said bimetalmember..]. .[.10. A controller according to claim 9, in which said mainsswitch has a switch slide and transversely extending contact armsthereon and in which said control cam means includes a cam for actuatingsaid switch slide..]. .[.11. A controller according to claim 10, inwhich said housing is rectangular or square and in which said switchslide lies diagonally in a corner of said housing..]. .[.12. Acontroller according to claim 10 in which said switch slide comprisesinsulating material and in which at least four metallic guides arrangedopposite one another in pairs are provided in said housing and extend atright angles to said switch slide for guiding said switch slide, saidguides defining thereon fixed contacts with which said contact armsco-operate and protruding through said housing to define connectingtabs..]. .[.13. A controller according to claim 1, in which said controlcam means combines a control body which has a control cam thereon, andan adjusting shaft which is received in a hole in said control body andprotrudes from the housing at the operating side thereof, and in whichthe housing has a bearing opening at its side remote from the operatingside and said control body has an integrally moulded bearing pin whichis journalled in said bearing opening..]. .[.14. A controller accordingto claim 1, which is adapted to operate with alternating current andwhich further comprises a diode and auxiliary switch means actuable bysaid control cam means for connecting said diode in circuit with saidheating means for said bimetal member, only in an upper power range butnot in a lower power range..]. .[.15. A controller according to claim 2in which an adjusting screw is associated with said longer limb andspring means is provided for biassing said longer limb against saidhousing via said adjusting screw..]. .[.16. A controller according toclaim 6 in which said compartment is provided with heat shield means..]..[.17. A controller according to claim 6 in which said compartment isprovided with ventilating means..]. .[.18. A controller according toclaim 14 in which said diode is located on a rear side of said housingremote from the operating side thereof and is disposed directly on saidauxiliary switch means..]. .[.19. A controller according to claim 18 inwhich said control cam means combines a control body which has a controlcam thereon, and an adjusting shaft which is received in a hole in saidcontrol body and protrudes from the housing at the operating sidethereof, and in which the housing has a bearing opening at its sideremote from the operating side and said control body has an integrallymoulded bearing pin which is journalled in said bearing opening..]..[.20. A controller according to claim 19, in which said bearing pin onsaid control body defines thereon a switching cam for said auxiliaryswitch means..]. .Iadd.
 21. A power controller for the substantiallystepless manual control of electrical a.c. power comprising:a housingin, and on which all components of the power controller are disposed;power switch means for a load; a bimetal member for intermittentlyoperating said power switch means; ambient temperature compensatingmeans for heating said bimetal member in dependence upon power suppliedto said load via said power switch means; manually operable controlmeans acting on said bimetal member; a diode for limiting power to saidheating means; auxiliary switch means, actuable by said control means,for enabling manual switching of said diode in circuit with said heatingmeans only in an upper power range, said heating means receiving onlyhalf wave power in an upper range but receiving full wave power in alower power range; a cam forming part of said manually operable controlmeans and including a sloped operating surface which compensates for acontrol discontinuity due to said switching of said diode when manuallyadjusting the control means between the upper and lower power ranges,whereby substantially stepless control is achieved despite theintermittent switching of the power. .Iaddend. .Iadd.
 22. A controlleraccording to claim 21, wherein said diode is in series with said heatingmeans and said auxiliary switch means is in parallel with said diode forshunting said diode in said lower power range. .Iaddend..Iadd.
 23. Acontroller according to claim 21, wherein said diode is located on arear side of said housing remote from the operating side thereof and isdisposed directly on said auxiliary switch means. .Iaddend..Iadd.
 24. Acontroller according to claim 23 wherein said control means comprises acontrol body which has a control cam thereon, and an adjusting shaftwhich is received in a hole in said control body and protrudes from thehousing at the operating side thereof, and wherein the housing has abearing opening at its side remote from the operating side and saidcontrol body has an integrally molded bearing pin journalled in saidbearing opening, said bearing pin on said control body defining thereona switching cam for said auxiliary switch means. .Iaddend.